Hi Mauro,
On Sunday 16 November 2008, Mauro Grauso wrote:
> Hi,
>
> I've just got a Logitech QuickCam E 3500 Plus (046d:09a4) that is an
> UVC device and is supported by the UVC kernel module. I'm under
> Kubuntu 8.10, kernel 2.6.27-8-generic #1 SMP.
>
> The problem is about the framerate, and specifically with the auto
> exposure feature of the camera. Basically when there's not enough
> light the camera is compensating (very well actually) and the
> framerate drops to 3fps, when there's daylight it still compensate and
> the framerate is about 15/20fps (@640x480).
That's quite usual with webcams. Cheap mass market CMOS sensors are not very
light sensitive and perform quite bad under low light conditions. Increasing
the exposure time automatically helps but at the cost of image quality (more
noise, blurry images, ...).
> The odd thing is that sometimes (but I haven't been able to reproduce
> it) the camera just doesn't use the auto exposure feature when I plug
> it in and, even if the image is darker, I get constant 30fps.
That's indeed weird. Auto-exposure should be enabled. How many times have you
encountered the issue ?
> Now I would really like to know how to turn off and on the auto
> exposure and white balance feature of the camera from the driver. If I
> try to turn off the auto exposure from the luvcview interface, I get
> "Set Auto Exposure off error" in the standard error.
Your luvcview version might be outdated. Could you try the latest one
(available from quickcamteam.net) or the uvcdynctrl command line tool (from
the libwebcam package available on the same website) ?
> For the record, when I plug the camera, syslog says:
> Nov 15 14:28:27 greywolf kernel: [11314.937051] usb 1-2: new high
> speed USB device using ehci_hcd and address 7
> Nov 15 14:28:28 greywolf kernel: [11315.178592] usb 1-2: configuration
> #1 chosen from 1 choice
> Nov 15 14:28:28 greywolf kernel: [11315.178862] uvcvideo: Found UVC
> 1.00 device <unnamed> (046d:09a4)
> Nov 15 14:28:28 greywolf kernel: [11315.209087] input: UVC Camera
> (046d:09a4) as
> /devices/pci0000:00/0000:00:02.1/usb1/1-2/1-2:1.0/input/input9 Nov 15
> 14:28:29 greywolf kernel: [11316.213276] 7:3:1: cannot get freq at ep 0x86
>
> Notice the last line!
>
> Sometimes the last line is slightly different, as follows:
> Nov 15 14:39:34 greywolf kernel: [11981.793172] 9:3:1: cannot set freq
> 16000 to ep 0x86
That's a usbaudio issue. Although not directly related to the video part, a
problem in the webcam audio implementation can of course influence video. I
wouldn't worry about it too much for now.
> And sometimes (often, but not always!) I also get the following in
> syslog when I plug the cam, but the error doesn't stop the cam from
> working:
> Nov 15 14:39:34 greywolf kernel: [11981.960176] uvcvideo: Failed to
> query (1) UVC control 1 (unit 0) : -110 (exp. 26).
I don't like that one, it reminds me of the Logitech firmware bug that is not
supposed to happen with that camera :-/
> Maybe the last line is about the snapshot button that is on the
> camera?
No, they are unrelated.
> Anyways the camera works even if I get these "soft" errors in syslog.
I would have thought the last error ("Failed to query...") would prevent the
driver from initialising the camera properly. Could you please show me all
messages printed by the driver to the kernel log when the problem occurs ?
> Help would be really appreciated. Thanks a lot to everybody.
Best regards,
Laurent Pinchart
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